Patella clamp apparatus

ABSTRACT

An improved patella clamp apparatus includes a scissor-like instrument frame having a pair of handles at one end portion. A patella holder and drill collet have gripping surfaces for holding a patient&#39;s patella therebetween during preparation for implantation of a prosthesis. The collet has arcuate slots for accepting the vertical ridge of the patella. A reamer or cutting instrument cuts a circular recess into the posterior face of the patella. The collet is supported by the frame and positioned opposite the elevator. The collet accepts a depth stop for referencing the posterior aspect of the patella. The collet provides a bore that supports a reamer or drill for forming the circular recess in the patella posterior surface.

BACKGROUND OF THE INVENTION:

1. Field of the Invention

The present invention relates to orthopedic surgical instruments, suchas surgical guides, surgical cutting instruments, and the like that areused to remove a predetermined amount of the patient's patella so thatthe patella can receive a prosthesis as part of knee joint replacementsurgery. Even more particularly, the present invention relates to animproved patella clamp apparatus that will allow the user to center thecut (eg. a reamer cut) on the patella vertical ridge by providing areamer collet that can be offset with respect to a patella holding jawthat cradles the patella during cutting.

2. General Background

In total knee arthroplasty, the patella usually requires a new articularsurface. This new surface can be obtained using an implant designed toconform to the geometry of the mating femoral implant. It is importantthat the patella position and tracking be reproduced with the implants.Thus, the instrument must be easy to use and yield reproducible results.

There are primarily two types of patella implants. One type requires aresurfacing of the patella. The other type requires that an inset orcavity be prepared for receiving the implant. With the resurfacingpatella implant, the patella requires a flat plane for placement of theimplant thereon. This plane is typically obtained by using a sawing or areaming technique.

A second type of implant is the inset patella implant. The inset patellaimplant requires an inset surface in the patella to place the implant.This surface can only be obtained by a reaming type instrument.

There are a number of issued patents that are concerned with patellaclamps in general. These prior art patella clamp instruments provide theuser with either a reamer-type cutting apparatus or a saw-type cuttingapparatus.

A recently issued patent, entitled "Method For Implanting A PatellarProsthesis", is issued to W. E. Mikhail, U.S. Pat. No. 5,180,384. TheMikhail patent discloses a method for preparing a patella for receivinga patellar implant and for implanting a prosthesis therein. An elongatedpassageway is formed in the patella which is then reamed to form acavity of a size and configuration to receive the patella prosthesisusing a cannulated reamer telescoped over a guide rod positioned in theelongated passageway.

The Whitlock et al. U.S. Pat. No. 5,147,365 discloses a patellaosteotomy guide comprising a plier-like appliance with curved jaws forgrasping a patient's patella. A row of teeth faces inwardly from thejaws. The teeth are generally of pyramid shape, but a vertex of eachtooth lies in a plane containing a bottom side of the respective jaw.Each of the jaws has an integral saw capture slot and the tips of thejaws are extended. A rotating, calibrated stylus measures the positionof the patella with respect to the integral saw capture slots. Therotating stylus also functions as a pivot or fulcrum about which thejaws and handles of the osteotomy guide rotate. Handles for theosteotomy guide are offset from the plane of the jaws. The rotatingstylus can be displaced up and down and then locked into a selectedposition using a draw bar and captured balls. A bowed retaining ringimparts a certain amount of pre-load to the stylus and draw bar assemblyto hold the assembly in a selected position.

A patella cutting clamp is disclosed in U.S. Pat. No. 5,108,401 issuedto Insall et al. The Insall device discloses a patella cutting clampthat comprises a pair of jaw members joined together in scissors-likerelation for pivotal movement relative to each other about a pivot axisintermediate their ends. Each jaw member has a handle portion extendingin one direction from the pivot axis and a jaw portion extending in theother direction. The jaw portions have edges facing each other that areshaped for engagement with opposite borders of a patella. Teeth alongthe patella-gripping edges grip and hold the patella firmly. Saw guideslots in the jaw portions lying in a common plane guide the saw when thesaw cut is made. A patella elevator member is attached to the jawmembers for movement along the pivot axis and has a platform portionadapted to engage the anterior aspect of the patella. A mechanism isprovided for establishing and maintaining a predetermined position ofthe elevator member relative to the jaw members and thereby positioningthe patella at a predetermined position relative to the saw guide slots.Another mechanism holds the jaw members in an adjusted position relativeto each other with the jaw portions engaging and holding the patella.

U.S. Pat. No. 5,129,908 issued to Thomas Petersen and entitled "MethodAnd Instruments For Resection Of The Patella" discloses a method ofperforming surgery to resect the patella for purpose of installing apatellar prosthesis, along with instruments used in such surgery. Theinstruments include a combined clamping device and reaming guide whichwhen clamped about the patella provides a guide for reaming the surfacethereof as well as a limit stop device designed to prevent reaming thepatella too deeply. The instruments also include a reaming devicedesigned to ream an annulus of material from the patella, leaving acentral raised portion for fixation of a patellar prosthesis.

A patellar clamp and reamer with an adjustable stop is disclosed in theHeldreth U.S. Pat. No. 5,129,907. The '907 patent discloses a patellarclamp and reamer for performing either a total surfacing procedure orinsetting procedure for preparing the patellar surface for a prostheticimplant, including an adjustable stop connected to the clamp andengaging a collar on the reamer shaft to space the reamer blade acalibrated distance from the clamp's reference jaw. The stop iscalibrated and includes indicator thereon in terms of the thickness ofpatellar bone to remain after resection.

The Burkinshaw et al. U.S. Pat. No. 5,021,055 discloses a patellar clampand surgical saw guide for preparing a patella to receive a prostheticarticulating surface on the patella's posterior side. A guide platesupports a saw block. The guide plate can be swiveled so that a sagittalsaw can be presented to the patella from any desired angle. The sawblock can be advanced or retracted axially so that more or less of thepatella will be cut away by the sagittal saw. A scale enables thelocation of the proposed cut to be quickly and accurately determined.Storage apparatus in a handle of the clamp holds different specializedtools for use during surgery.

A patella clamp is disclosed in the Petersen U.S. Pat. No. 4,706,660which includes a fixed jaw having a spike centrally disposed on a partspherical surface with this spike being axially aligned with areciprocating plunger. The plunger is operated by a second handlepivotally disposed with respect to the first handle and spring biasingmeans between the handles biases them in a direction of separation ofthe plunger and spike.

Another Petersen U.S. Pat. 4,633,862 entitled "Patellar ResectionSawguide" discloses a method and instruments for the installation of apatellar button prosthesis. The first instrument consists of a saw guideincluding gauges integrally attached thereto which aid the surgeon indetermining whether the patella has been grasped at the correct locationwith respect to the anterior and posterior sides thereof, whichdetermine for the surgeon whether adequate bone stock will remain afterresection of the patella, and which are chosen to correspond with theparticular thickness of the patellar button which is to be installed.The second instrument consists of a drill guide including structureenabling its attachment to one of the jaws of the saw guide so that thesaw guide may be retained in position about the patella after resection.A further instrument usable with the present invention consist of adrill bit including a collar which is provided to interact with holesformed in the drill guide to as to limit the depth of the holes whichare drilled in the patella for the purpose of installation of thepatellar button. Finally, a patella clamp is provided which includes asingle moveable jaw limited in its movement solely to reciprocation,which clamp is utilized to install the patellar button onto the resectedpatella. The disclosed method involves the use of the above describedinstruments for the purpose of installation of a patellar buttonprosthesis.

The Shapiro U.S. Pat. No. 4,565,192 discloses a device for cutting aportion of a patella during knee surgery in which the articular surfaceof the patella along with a portion of the bone of the patella is cutaway for implantation of a prosthesis. The device disclosed provides afixed clamping member and an adjustable clamping member which clamp thepatella and space from the patella a support surface for an oscillatingsaw used in the cutting of the patella. The precise plane of cut isprovided by the use of a placement aid which is used according to themethod of the present invention. The placement aid positions the supportsurface a precise depth below the articular surface of the patelladuring the clamping procedure, which clamping procedure alsohorizontally levels the support surface and the device so that all cutsthrough the patella are made in a perfectly horizontal place. Spacersare also provided which are mountable over the support surface and areused to allow for progressively deeper cuts to be made in the patellathrough parallel horizontal planes of cut by allowing interchanges ofone spacer for another of less thickness. Each spacer has its own flatsurface that allows support of the oscillating saw thereon for cuttingthrough the patella during that particular cut as defined by thethickness of the spacer used.

SUMMARY OF THE INVENTION:

The present invention provides an improved patella clamp apparatus thatallows a surgeon adjustability when gripping the patient's patella sothat the rotary cut can be placed at the patella ridge even if thepatella ridge is not the "center" of the patella.

The apparatus of the present invention includes an instrument framehaving handles for manually supporting the frame. The patella can beheld during a surgical preparation of the patella with a holder mountedon one arm of the frame and a guide that slidably engages the other armof the frame.

The guide member has teeth for engaging the patella and recesses thatconform generally to the shape of the patella ridge. A holding surfaceon one of the arms provides a concave surface for cradling the patellaand a plurality of spikes for gripping the patella.

A drill guide is movably supportive upon the frame and positionedgenerally opposite the holding surface. The guide is movable along aline generally parallel to the plane of the holding surface and tomultiple adjustment positions relative to the center of the holdingsurface.

The guide provides a cylindrically shaped bore that supports a rotaryreamer cutting instrument that prepares the patella posterior surface toreceive a prosthetic patella, generally circular.

Lateral movement of the guide upon the frame defines a position of cutsto be made into the patient's patella so that the cuts can be centeredon the patient's patella ridge, not necessarily the center of thepatella.

An adjustment is provided for defining the depth of cut. The adjustmentincludes a stop housing mounted on a drive shaft of the reamer. The stophousing has a lower surface that abuts the upper surface of the guide.

A gauge is provided for setting the depth of cut by setting a distancebetween the top of the guide and the bottom of the stop housing when thecutting instrument just touches the patella tissue to be cut. Also thegauge determines diameter. The gauge can include a number of thicknessesfor defining different depths of cuts such as for example 10 mm, 12 mm,and 14 mm. The gauge also determines the diameter of the prosthesis tobe used such as 23 mm, 26 mm, or 29 mm. For example, if the surgeonwants to use a 26 mm diameter prosthesis, the gauge automatically sets a10 mm depth of cut.

The frame can include a pair of spaced apart arms having handles thatallow the surgeon to hold both handles simultaneously.

A spring urges the arms apart and a threaded shaft with a nut mountedthereon defines the distance between the arms. Further, a tightening ofthe nut upon the threaded shaft forces the holder and guide together sothat the teeth on the guide bite into the patella on one side and thespikes of the holder bite into the patella on the other side for a firmgrip.

An adjustment of depth of cut is preferably provided by a stop assemblymounted on the drive shaft of the reamer. A plurality of spaced apartteeth with grooves therebetween are provided on the drive shaft of thereamer. The reamer stop housing can be attached to selected grooves bypushing a knob on a stop guide that is movable with respect to the stophousing. Thus, the surgeon simply pushes the knob to release the stopfrom the drive shaft, moves the stop housing vertically to a desiredposition, and then releases the stop guide so that it bites into thedrive shaft, registering into one of the grooves.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention, reference should be had to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like parts are given like reference numerals, and wherein:

FIG. 1 is a perspective view of the preferred embodiment of theapparatus of the present invention;

FIG. 2 is a fragmentary sectional view of the preferred embodiment ofthe apparatus of the present invention illustrating the connectionbetween the instrument frame and guide assembly;

FIG. 3 is a top fragmentary view of the preferred embodiment of theapparatus of the present invention;

FIG. 4 is an elevational fragmentary view of the preferred embodiment ofthe apparatus of the present invention;

FIG. 4A is a fragmentary sectional elevational view illustrating thereamer drive shaft and stop member in an engaged position;

FIG. 5 is a partial elevational view of the preferred embodiment of theapparatus of the present invention illustrating the guide portionthereof;

FIG. 6 is a top sectional view of the guide portion of the preferredembodiment of the apparatus of the present invention;

FIG. 7 is a side, partial sectional view of the guide portion of thepreferred embodiment of the apparatus of the present invention;

FIG. 8 is a bottom view of the guide portion of the preferred embodimentof the apparatus of the present invention;

FIG. 9 is a partial view of the preferred embodiment of the apparatus ofthe present invention illustrating a portion of the instrument frame;

FIG. 10 is a partial view of the preferred embodiment of the apparatusof the present invention illustrating a portion of the instrument frame;

FIG. 11 is a partial fragmentary perspective view of the preferredembodiment of the apparatus of the present invention illustrating thereamer stop portion thereof;

FIG. 12 is a fragmentary sectional view of the preferred embodiment ofthe apparatus of the present invention illustrating a portion of thereamer stop;

FIG. 13 is a top view of the reamer stop housing portion of thepreferred embodiment of the apparatus of the present inventionillustrating a portion of the reamer stop;

FIG. 14 is a fragmentary sectional view of the preferred embodiment ofthe apparatus of the present invention illustrating a portion of thereamer stop;

FIG. 15 is a fragmentary top view of the preferred embodiment of theapparatus of the present invention illustrating a portion of the reamerstop; and

FIG. 16 is a perspective view illustrating the gauge portion of thepreferred embodiment of the apparatus of the present invention;

FIGS. 17-19 are perspective schematic views that illustrate the patellaclamp apparatus of the present invention in use when preparing apatient's patella to receive a surgical implant.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows generally the preferred embodiment of the apparatus of thepresent invention designated generally by the numeral 10. Patella clampapparatus 10 includes an instrument frame 11 that comprises a pair ofspaced apart and generally parallel arms 12, 13. The arms are joined bya pair of diagonal struts 15, 16 that intersect at pivot 14. Each of thearms 12, 13 includes a distal end portion 17A, 18A respectively thatcarry a guide member 21 and a patella holder 34 as will be describedmore fully hereinafter.

A threaded rod 19 is attached to the lower arm 13 at weld 20. Guidemember 21 slides with respect to the central longitudinal axis of upperarm 12 as indicated by the arrows 21A in FIG. 4. Guide member 21provides a cylindrically shaped bore 22 that holds a rotary reamer 60during surgical preparation of the patient's patella 40. The guidemember 21 provides a pair of spaced apart curved tooth sections 24 witha pair of arcuate recesses 23 therebetween. The recesses 23 conform tothe patella ridge 41 during surgical preparation (reaming) of thepatella as the reamer cutting blade element 61 centers its cuts on thepatella ridge 41 (see FIG. 4).

Guide member 21 includes a longitudinally extending slot 25 that fitsthe threaded member 19 as shown in FIGS. 1, 3, and 4. The guide member21 also includes a pair of longitudinally extending flanges 26, 27 thathold the guide member 21 to the upper arm 12 as shown in FIG. 2. A nut28 can be used to adjust the distance between upper and lower arms 12,13 by rotating the wing nut 28 upon threaded member 19. Wing nut 28threadably engages member 19 shown in FIG. 4. Spring 29 urges the upperand lower arms 12, 13 apart. However, the wing nut 28 acts a stop,limiting the distance that the arms 12, 13 can move away from eachother.

The scissor-like diagonal struts 15, 16 maintain the arms 12, 13 in agenerally parallel relationship. The diagonal struts 15, 16 are eachpinned at pinned connection 56, 57 respectively to the arms 13, 12respectively.

Each end portion of each strut 15, 16 travels in a slot that extendslongitudinally along the arms 12, 13. In FIGS. 1, 9, and 10, struts 15can be seen fitted to the longitudinally extending slot 32 of arm 13 andslot 31 of upper arm 12. Similarly, diagonal strut 16 fits slot 33 ofthe lower arm 13 and the slots 30 of upper arm 12. The diagonal member15 thus extends between the slots 31 (of upper arm 12) and 32 (of lowerarm 13). The diagonal member 16 extends between slot 30 of arm 12 andslot 33 of arm 13. The arms 15, 16 slide in the slots 31, 33respectively. Each of the respective diagonal members 15, 16 is pinnedat pinned connections 56, 57 respectively to arms 12, 13. The armproximal ends 17B, 18B each provide laterally extending pins 60 thatengage the slots 58, 59. Slots 58, 59 communicate with the slots 31, 33.

A patient's patella 40 typically has a projecting portion known as thepatella ridge 41. The patella ridge 41 is not always located at thecenter 40A of the patient's patella. As shown in FIG. 4, the patellaridge 41 can be offset with respect to the actual center 40A of thepatient's patella 40. The apparatus 10 of the present inventionaccommodates for such an offset by allowing the guide 21 to adjustlongitudinally along upper arm 12. Thus, a rotary reamer 60 can bedesirably centered on the patient's patella ridge 41 as shown in FIG. 4before the surgeon activates the reamer to cut an opening for receivinga patella implant.

Lower arm 13 provides a holder 34 for holding the patient's patella 40.Holder 34 provides a concavity 37 lined with a plurality of spikes 35 asshown in FIG. 10. The spikes 35 extend upwardly for engaging the patella40 which is placed under the cylindrical wall 36 of guide 21, andgripped by teeth 24. Reamer 60 is then placed within the bore 22 ofguide 21. An opening 38 in upper arm 12 accepts threaded member 19. Oneor more transverse, internally threaded openings 39 in guide member 21can be used for holding externally threaded set screws. Set screws canbe optionally used for immobilizing guide 21 with arm 12 once aparticular location of guide 21 is selected. Wing nut 28 alsoimmobilizes guide 21 once it is tightened to force teeth 24 againstpatella 40 and its holder 34.

In FIGS. 1, 4, 4A, and 11-15, reamer stop housing 42 is shown. In FIG.11, housing 42 and stop guide 50 are viewed from below for betterillustrating pin 48 and slot 55. The reamer stop housing 42 mounts uponreamer 60 at drive shaft 62 and defines the depth of cut to be made by ablade element 61 at the lower end of reamer 60. Reamer stop housing 42includes a larger diameter cylindrically-shaped opening 43 and a smallerdiameter cylindrically-shaped opening 44. The openings 43, 44 share acommon axis 58.

Annular shoulder 45 is positioned at the intersection of opening 43, 44.Vertical bore 46 intersects axis 58 at approximately right angles asshown in FIGS. 12 and 13. Reamer drive shaft 62 fits vertical bore 46,tracking its central longitudinal axis 59.

Pin opening 47 accepts stop pin 48. Stop pin 48 extends into smalldiameter cylindrical opening 44 and into horizontal slot 55 of stopguide 50. In this fashion, the user can push on the stop guide 50 inorder to release the drive shaft 62 of rotary reamer 60 allowing forvertical, depth of cut adjustment. Coil spring 49 surrounds the stop 54of stop guide 50, registering in annular slot 63. Spring 49 also bearsagainst annular shoulder 45 urging the stop 54 into engagement with theouter surface of shaft 62 thereby setting the position of housing 42relative to drive shaft 62 (see FIG. 4A).

In order to select a particular depth of cut, the user pushes knob 51 ofstop guide 50 overcoming spring pressure supplied by coil spring 49.This disengages the stop 54 from the outside surface of drive shaft 62.This also removes the stop 54 from engaging the annular spaces 64between the adjacent teeth 65 of drive shaft 62. A gauge 66 can be usedto measure the depth of cut by placing the gauge between the uppersurface 67 of guide member 21 and the lower surface of 68 of stophousing 42. Releasing the stop guide 50 at the desired position thenaffixes stop 50 to a space 64 between adjacent teeth 65.

FIGS. 17-19 illustrate the surgical method of the present inventionusing the apparatus 10 of the present invention. In FIG. 17, patellaclamp apparatus 17 has been placed in an inoperative position with thepatient's patella 40 in between holder 34 and the teeth of guides 21.The surgeon loosens the wingnut 28 as shown and adjusts the guide member21 until the recess 23 of guide 21 is placed at the patient's patellaridge 41. The surgeon then tightens the wingnut 28 until the teeth 24 ofguide 21 firmly grips the patella on one side and the spikes 35 ofholder 34 on the opposing side of the patella 40.

The surgeon then uses the gauge 66 to select a particular diameterprosthesis and to also set the appropriate depth of cut. The surgeonuses the gauge (see FIGS. 4 and 16) to select a diameter and depth ofcut that the surgeon believes is appropriate for the particular patella40 being prepared. The gauge 66 provides a plurality of gauge arms 69,71, 73. These arms can extend from a central hub 75 or can be mountedparallel on a rectangular member (see FIG. 18). Each of the armsprovides a recess 70, 72, 74 respectively that fits about the driveshaft 62 of rotary reamer 60. A particular gauge arm 69, 71, 73 is of aparticular thickness. For example, thicknesses of 10 mm, 12 mm, and 14mm are exemplary. In FIG. 4, a 14 mm thickness arm has been placed inbetween the upper surface 67 of guide member 21 and the lower surface 68of stop housing 42. This 14 mm thickness corresponds to a prosthesisdiameter of 29 mm.

In the preferred embodiment, the gauge 66 is configured as shown in FIG.16. However, the gauge can be an elongated rectangular structure asshown in FIG. 18, having three gauge arms extending at right anglesthereto. In FIG. 16, the gauge arm 69 has a thickness of 10 mm and arecess 74 registering with the drive shaft 62. The gauge arm 61 has athickness of 14 mm and a recess 72 for registering with the drive shaft62. The gauge arm 73 has a thickness of 12 mm and a recess 74 forregistering with the drive shaft 62.

In FIG. 19, the stop guide 50 has been engaged so that the stop 54engages one of the annular teeth 65 or annular groove of drive shaft 62.This affixes the position of reamer stop housing 42 and moreparticularly its under side 67. The surgeon then places the reamer 60 inthe bore 22 and allows the reamer cutting blade elements 61 to engagethe patient's patella 40. A rotary driver (not shown) is used to powerand rotate the reamer 60. The cutting elements 61 surgically cut thepatella 40 to perform a circular recess that will accept a patellaimplant. The depth of cut is governed by the registration of undersurface 67 of stop housing 42 against the upper surface 67 of guidemember 21.

The following table lists the parts numbers and parts descriptions asused herein and in the drawings attached hereto.

    ______________________________________                                        PARTS LIST                                                                    Part Number     Description                                                   ______________________________________                                        10              apparatus                                                     11              instrument frame                                              12              upper arm                                                     13              lower arm                                                     14              pivot                                                         15              diagonal strut                                                16              diagonal strut                                                17A             distal end                                                    17B             proximal end                                                  18A             distal end                                                    18B             proximal end                                                  19              threaded rod                                                  20              weld                                                          21              guide member                                                  21A             arrows                                                        22              bore                                                          23              arcuate recess                                                24              toothed sections                                              25              slot                                                          26              flange                                                        27              flange                                                        28              wingnut                                                       29              spring                                                        30              slot                                                          31              slot                                                          32              slot                                                          33              slot                                                          34              holder                                                        35              spike                                                         36              cylindrical wall                                              37              concavity                                                     38              opening                                                       39              opening                                                       40              patella                                                       40A             center of patella                                             41              patella ridge                                                 42              reamer stop housing                                           43              larger diameter opening                                       44              smaller diameter opening                                      45              annular shoulder                                              46              vertical bore                                                 47              pin opening                                                   48              stop pin                                                      49              coil spring                                                   50              stop guide                                                    51              knob                                                          52              cylindrical section                                           53              vertical opening                                              54              stop                                                          55              horizontal slot                                               56              pinned connection                                             57              pinned connection                                             58              axis                                                          59              axis                                                          60              rotary reamer                                                 61              blade element                                                 62              shaft                                                         63                                                                            64              annular groove                                                65              annular tooth                                                 66              gauge                                                         67              upper surface                                                 68              lower surface                                                 69              gauge arm                                                     70              recess                                                        71              gauge arm                                                     72              recess                                                        73              gauge arm                                                     74              recess                                                        75              hub                                                           ______________________________________                                    

Because many varying and different embodiments may be made within thescope of the inventive concept herein taught, and because manymodifications may be made in the embodiments herein detailed inaccordance with the descriptive requirement of the law, it is to beunderstood that the details herein are to be interpreted as illustrativeand not in a limiting sense.

What is claimed as invention is:
 1. A patella clamp and rotary cuttingapparatus comprising:a) an instrument frame that includes handle meansfor manually supporting the frame the frame having proximal and distalend portions; b) a holder for manipulating the patella during a surgicalpreparation of the patella by engaging a side of the patella oppositethe side to be surgically cut, said holder having a patella holdingsurface that defines a plane for holding the patella in a desiredposition, said holding surface having a center; c) a drill guide movablysupported upon the frame and positioned generally opposite the patellaholding surface, the guide being movable along a line generally parallelto the plane of the holding surface into multiple positions relative tothe center of the patella holding surface; d) the drill guide providinga bore; e) a rotary cutting instrument that fits the drill guide borefor surgically preparing the patella posterior surface to receive aprosthetic patella; f) wherein movement of the drill guide upon theframe enables a surgeon to offset the central axis of the rotary cuttinginstrument with the center of the holder to define the position of cutsto be made both proximally and distally of the rotary cutting instrumentinto the patient's patella in relation to the center of the patella; g)the rotary cutting instrument registering with the guide at apreselected depth of cut position relative to the patella so that theguide prevents the cutting instrument from cutting too deeply into thepatella; and h) the rotary cutting tool having an adjustment thereon fordefining the depth of cut made by the cutting instrument into thepatella, enabling a surgeon to adjust the depth of cut on the rotarycutting tool while the frame is holding the patella.
 2. The apparatus ofclaim 1 wherein the handle means comprises a pair of opposed handles. 3.The apparatus of claim 1 wherein the frame comprises a pair of framehalves.
 4. The apparatus of claim 1 wherein the holding surface isgenerally rounded.
 5. The apparatus of claim 1 wherein the guide isgenerally cylindrically shaped.
 6. The apparatus of claim 1 wherein theframe comprises a pair of frame halves that are parallel to one another.7. The apparatus of claim 1 wherein the rotary cutting instrumentincludes a drive shaft.
 8. The apparatus of claim 7 wherein theadjustment includes annular adjustment positions spaced along the driveshaft.
 9. The apparatus of claim 1 further comprising feeler gauge meansfor measuring the depth of cut.
 10. The apparatus of claim 1 wherein theadjustment comprises a stop assembly mounted on the rotary cuttinginstrument for stopping movement of the cutting instrument relative tothe drill guide.
 11. The apparatus of claim 10 wherein the adjustmentincludes a stop assembly mounted on the cutting instrument andpositioned to abut the drill guide for limiting the depth of cut.
 12. Apatella clamp and rotary cutting apparatus comprisinga) an instrumentframe that includes handle means for manually supporting the frame theframe, having proximal and distal end portions and a patella holder witha center; b) a drill guide collet, supported at one end of theinstrument frame, the collet providing a bore that supports a rotarycutting instrument for preparing a patient's patella posterior surfacefor receiving a prosthetic patella; c) a rotary cutting instrument thatfits the grill guide collet; d) the rotary cutting instrument having anadjustment thereon for enabling a surgeon to set a desired depth of cutinto the patient's patella; e) the rotary cutting instrument having acenter of rotation; and f) the frame and drill guide collet beingslidably connected for adjusting the position of center cut bothproximally and distally relative to the center of the patella holder.13. The apparatus of claim 12 wherein the frame comprises a pair offrame arms that are generally parallel.
 14. A patella clamp and rotarycutting apparatus comprising:a) an instrument frame that includeshandles for manually supporting the frame, the handles including a pairof frame arms, the frame having proximal and distal end portions and apatella holder with a center; b) a collet, supported by the frame at oneof the arms and providing a bore; c) a rotary cutting instrument havinga center of rotation that fits the collet for preparing the patellaposterior surface to receive a prosthetic patella; d) an adjustablemember for moving the collet along one of the frame arms into multiplepositions relative to the frame so that said center of rotation isadjustable both proximally and distally relative to the center of thepatella holder; e) the rotary cutting instrument having an adjustablestop thereon for defining the depth of cut of a rotary cuttinginstrument into the patella, enabling a surgeon to adjust the depth ofcut on the rotary cutting tool while the frame is holding the patella.